This invention relates to an intake air filter for the internal combustion engine of a motor vehicle, in which
An intake air filter of this type is disclosed in Engel et al., U.S. Pat. No. 4,720,292. It comprises a cylindrical housing which has an inlet opening for unfiltered air on its circumference, and which is provided with an outlet for filtered air on one end face. A cartridge or filter insert is arranged inside the housing. This filter insert extends over the entire axial length of the housing and has at its end facing the clean air outlet a gasket which lies directly adjacent the end face of the housing. A tubular projection extends into the interior of the housing. The filter insert is additionally supported on this projection, thus securing the filter insert radially within the housing. The housing is closed at the end opposite the air outlet by a cover. The cover also serves to exert a force on the filter insert toward the air outlet and thus holds the filter insert in its installed position. The axial position of the filter insert is thus directly fixed by the cover.
This construction necessitates very high accuracy both in the length of the filter insert and in the length of the housing, so that a uniform force is always exerted on the filter insert and there is no danger that the filter insert can move in the axial direction and possibly become displaced. Since no guidance is provided on the housing for the filter insert, the insert can become skewed when installed and can be clamped in a skewed position by the cover. The result will be that a proper seal between the raw air space and the clean air space will no longer exist, so that dust-laden air can enter the clean air space and thence into the motor.
Another intake air filter for internal combustion engines, compressors and other air-aspirating machines is disclosed in German Utility Model No. DE-G 73-21,762. This filter has two filter inserts and is provided with a central threaded bolt anchored in the clean air tube which serves to fasten the filter inserts in place. This bolt is passed through the openings into the cover disks of the filter and tightens the filter inserts axially against the housing parts by means of nuts threaded on it. To fix the filter inserts in correct position, abutments are provided on the bolt and the cover disks lie on the abutments. This fastening arrangement requires a very high accuracy of the abutments with respect to the surface on which the filter inserts lie in the housing. Furthermore, high accuracy in the length of the filter inserts is also required in order to assure reliable sealing of the end face of the filter insert that lies adjacent the clean-air outlet. This need for high accuracy leads to an unreasonably high cost of the filter inserts which must be frequently replaced.
Another disadvantage of the threaded bolt arrangement is that the bolt has to be fastened within the air outlet on the clean air side. If the housing is made of sheet metal, this may be possible, for example, by spot welding. If the housing is made of plastic and the clean air outlet in integrated into the housing, a threaded bolt can be fastened to the housing only if additional reinforcing ribs, embedded metal pieces, or and the like are provided.
Even in the case of a very complex design, there is a danger that the creep characteristic of the plastic over a long period of time might cause the holding force on the filter insert to diminish, so that the seal between the raw air side and the clean air side is at risk due to the possibility of an unnoticed loosening of the filter insert.